Bund / Stockpiling solution
It happens often that invasive species interfere with proposed developments, whether it happens to be housing or infrastructure. Bund installations offer a potentially cost effective solution to offsite removal. The process involves excavating the materials from the original location and stockpiling in a bund installation at an alternative location on site, thus allowing the original development to proceed as planned.
The contaminated soil stockpiled is then monitored and treated through a herbicide treatment program over several years.
These bunds or stockpiles can often be worked into the proposed landscaping for developments e.g., green areas or wind breaks etc.
Advantages of bund / stockpile:
- Cost effective.
- Allows development works to be undertaken whilst treatment takes place elsewhere on the site.
Disadvantages of bund / stockpile:
- Requires area on site set aside for implementation of bund.
- Restrictions remain in bund area.
- Soil from stockpile must remain on site.
Burial and Deep Cells
An alternative to stockpiling is deep burial of plant materials and contaminated soil. The process involves creating a deep cell, lined with a geosynthetic root membrane, and burial of the materials within. Two main types of burial can occur:
- Fully encapsulated cell: The option for a fully encapsulated cell consists of the bottom, sides, and top of cell being lined with a root barrier. This ensures all IAPS contaminated material is completely encapsulated underground. Normally, a sufficient infill coverage of needs to be achieved on top of the cell to protect it from burrowing animals.
- Capping of cell: Capping the cell refers to lining of the top of the cell only. This means the sides and bottom of the burial cell are not lined. Sufficient infill coverage of needs to be achieved to make this a viable option.
Advantages of burial:
- Does not require a set-aside area for control as a bund solution does.
- Work can continue immediately after burial
Disadvantages of burial:
- Limits future excavations of area above burial site
Excavation and off-site removal
Where it is required, contaminated soil material can be removed from site by a licenced haulier to be disposed of at a suitably licensed landfill. Suitable permits are required for the transportation and disposal of IAPS materials offsite. This approach can be prohibitively expensive if dealing with large quantities and once disposal and transportation costs are factored in.
Advantages of Excavation and off-site removal:
- Work can continue immediately after removal.
- No restrictions remain on site.
Disadvantages of Excavation and off-site removal:
- Can be prohibitively expensive.
Root barrier membrane is strong, flexible, sheeting of Polyethylene and is used to suppress the growth of Japanese Knotweed and other invasive species. It acts as a barrier between contaminated material and clean soil and prevents the plant from spreading. It is used in deep cell formation where it is used to either fully encapsulate excavated contaminated material or to cover the top of the contaminated material in the cell.
Root membranes can also be installed vertically to isolate Japanese knotweed or other invasive species from a site boundary. It can also be used to protect services.
In most cases, the root membranes require a buffer layer of protective material (e.g., sand) on either side to protect it from puncturing or piercing.